1. Field of the Invention
The present invention relates to computer networks in general and, in particular, to electrical power management in said networks.
2. Prior Art
The reduction of electrical power consumption in computer networks is a desirable goal which is met by using so called "Green PCs" (Personal Computers) and specially formatted LAN (Local Area Network) packets for waking up the PCs. Green PCs are built with power saving capabilities which allow them to power off or reduce power consumption (sleep) during periods of non-use.
In order to restore the PCs to full power status (wake), a specially formatted frame termed MAGIC PACKETS.RTM., Wake-On-LAN or similar names is generated by a network management PC and transmitted on the LAN. The specially formatted frame includes the Destination Address (DA) of the PC to be awakened and the DA repeated several times in the data field of the frame. Even though all PCs on the LAN see the frame, only the one whose address is in the frame is restored to full power.
U.S. Pat. Nos. 5,396,636 and 5,404,544 are examples of the prior art using specially formatted frames to distribute "wake-up" information. In both patents, computers are switched from a low power consumption (sleep) mode to full power consumption (wake) mode based upon specially formatted frame received over the network.
Even though the prior art power management procedures and devices work well for their intended purposes, they suffer drawbacks which the below described invention addresses and corrects.
One of the drawbacks with the prior art is that the MAC address of the station has to be known. If the individual MAC address of a station is unknown, it cannot be awakened. There are times when the Network Manager may want to awaken a station, even though its MAC address is unknown. For example, the Network Manager may wish to awaken a particular NETBIOS station identified by its NETBIOS name. The current state of the art does not allow this freedom.
Another drawback is that the prior art does not allow the awakening of multiple stations with a single frame transmission. There are times when a Network Manager may wish to do so.
The inability of the prior art to awaken a station whose address is unknown or to awaken multiple stations with one frame transmission imposes unnecessary restrictions on the Network.
A straight forward solution to the above drawbacks would be for a technician to locate the station and use a manual approach such as hitting a key to "wake the station up". This approach is unacceptable because, among other reasons, it requires human intervention that is subject to errors or the station may be difficult to reach, remotely located, or behind a locked door.